In a public switched telephone network (PSTN), an electronic switching machine at the central office (CO) switches and routes telephone calls to the end telephone user (subscriber). In the past, each subscriber was connected to the CO by an individual pair of copper wires. As the number of subscribers grew, the number of wires between them and the CO grew accordingly. In modern networks, the number of wires or fiber-optic cables needed to service a group of individual subscribers can be reduced by multiplexing a group of subscribers' communications over one line. That is, each individual subscriber's communication is assigned a unique channel which is then combined with the channels from other subscribers and transmitted on the transmission link. Each transmission link has a maximum number of channels which can be handled simultaneously.
The number of transmission links necessary to service a group of subscribers can further be reduced by using a process called concentration. In concentration, more subscribers than the transmission link is physically capable of handling are connected to an electronic concentrator. Because it is statistically unlikely that all of the subscribers will actually use their telephones at the same time, the concentrator is able to select only those which are in use, the number of which is probably less than o equal to the maximum capability of the multiplexed transmission link, and connect them to the transmission link.
The multiplexing and concentration functions are typically performed by electronic equipment which is located between the CO and the subscriber. This equipment is referred to as a remote terminal (RT). In addition to the multiplexing and concentration functions, some of the more sophisticated RTs are also capable of receiving and processing some of the CO switching machine's work in order to reduce the latter's workload. As the cost of electronics and optical fiber decreases, and the demand for services that require greater transmission bandwidth than can be offered over traditional copper telephone lines increases, the RTs are moved ever closer to the subscriber. It is expected that an RT will eventually become the multiplexing and concentration site for a number of smaller RTs that are located at the subscriber's premises. These smaller RTs will be comprised of Optical Network Terminals (ONTs), which allow optical fiber to link the subscriber's premises with the RT.
The RTs and ONTs are all typically controlled by software and/or firmware, so that system faults can be corrected, and enhancements added, without extensive hardware replacement. Despite the efficiencies gained by this implementation, however, it would still be very expensive to send a repair person to each subscriber location in order to install new firmware into the subscriber's ONT.
Consequently, it is an object of the present invention to provide a mechanism which allows the new ONT firmware to be downloaded to a group of ONTs from a common location (e.g., the CO or the RT), using the transmission link that is commonly used for subscriber communication.
It is a further object of the present invention to provide a mechanism which allows the ONT to initiate the firmware download operation by signalling to the RT via an overhead channel which is not used for conveying subscriber communications.
It is still a further object of the present invention to provide a mechanism which allows the RT to initiate the firmware download operation by signalling to the ONT via an overhead channel which is not used for conveying subscriber communications.
It is still a further object of the present invention to convey the firmware from the RT to the ONT in a format which is compatible with the format normally used for conveying subscriber communications via the communications link.
It is still a further object of the present invention to download firmware from the RT to the ONT in a format which simplifies the hardware which performs the download operation.
It is still a further object of the present invention to detect transmission errors which corrupt the firmware transmitted by the ONT.
It is still a further object of the present invention to provide for the retransmission of those portions of the firmware which were corrupted in the transmission process.
It is still a further object of the present invention to provide a timeout mechanism to prevent a communication "lock-up" between the RT and ONT due to a hardware failure during the transmission and handshaking portion of firmware download.